This invention relates to nutrient supply systems for controlled environment agriculture installations and more particularly to nutrient feed regulation systems providing automatic control of nutrient flow rate to and through the plant growth containers in nutrient film agriculture installations.
The recent development of nutrient film techniques for plant husbandry has opened new opportunities for the production of horticultural crops. Nutrient film techniques differ from the more conventional hydroponic techniques, in which the plant root masses are arranged to be totally immersed in the nutrient solution either costantly or periodically, principally in that in nutrient film agriculture the plant roots are wetted only by contact with a small stream of liquid nutrient. Capillary attraction or wicking then is relied on to extend the nutrient-wetted area over and through the entire root mass. Nutrient supply commonly is accomplished by positioning the plant roots in long troughs or gullies formed of metal, plastic or the like, and flowing a thin stream of liquid nutrient along the bottom of the gulley permitting the stream to contact each of the plant root bundles as it flows along. Nutrient not absorbed by the plant roots drains from an open end of the gulley, which normally is slanted sufficiently to effect a gravity-induced flow of the nutrient along its length. The excess nutrient which drains from the gullies is recycled, usually after any needed replenishment of its compositional elements.
The nutrient stream may desirably be small and the flow rate kept quite low in nutrient film systems, since only enough nutrient is needed to wet the portion of the root mass immediately adjacent to the bottom of the gulley in which the plant is located. Accurate and reliable control of nutrient flow rate is required, however, because if the flow rate becomes inadequate the roots may dry excessively causing damage or even destruction of the plant. This control problem becomes much more difficult where there are a large number of gullies to which nutrient is fed by a common supply system, as will commonly be the case in large installations. In such installations it becomes very difficult to maintain precise equalization of the nutrient feed rates to each of the gullies in the system, yet such equalization is essential if some gullies are not to receive inadequate nutrient supply while others have an excess.
Present nutrient film installations generally depend upon capillary tubes connected between a supply header tube and the individual gullies to regulate the nutrient flow rate to each gulley. Where the header tube is long and feeds a large number of gullies variations in pressure may exist along the header length, and in installations in which the gullies are tiered or otherwise disposed at different heights, differences in hydrostatic pressure of the nutrient supply to the capillary tubes result in considerable variation in nutrient flow rates from gulley to gulley. Capillary tubes may also tend to clog over a period of time, due to deposits of impurities or precipitates from the nutrient solutions in the tubes, and this further aggravates the problem of inequality of nutrient distribution as between the different gullies.
Precision flow regulators of various kinds are commercially available, of course, and could be used in nutrient film agriculture installations. Their initial cost tends to be high, however, and their maintenance costs may likewise be high due to the problem character of the nutrient liquids which they must handle and the large number of regulators required.
The present invention is directed to a nutrient supply system which minimizes these problems common to conventional nutrient film agriculture installations, and which achieves this objective at relatively modest cost both in terms of initial installation expense and in terms of maintenance expense over long use periods.